C2's render is quad only so the vertex shader would have only 4 vertices to manipulate, so there wouldn't be much variety in shaders. Also there is the overhead of changing the shader and sending the parameters to the gpu. My argument is it would probably be slower with such a low vertex count.
Vertex shaders could be useful if a plugin was made that had a high polygon mesh, but you'd be doing custom webgl to render that anyway so that would be the place to do it.